Scaling and Curvature Effects on the Damage Tolerance of Impacted Composite Sandwich Panels

Abstract

An experimental program was conducted to investigate the effects of specimen width and specimen curvature on the residual compression strength of composite sandwich panels after low-energy impact. Flat and curved (1.1 m radius) specimens of three widths (83, 152, and 305 mm) were manufactured from thin-gage (four plies) graphite/epoxy facesheets and 25.4-mm-thick Nomex core. A drop mechanism was used to create barely visible impact damage on one facesheet of the panels (convex face of the curved panels) maintaining the energy level as constant in all cases. All specimens were then loaded axially in compression to failure. Above a certain panel width, the panel width and curvature had noeffect on the ultimate strength of the panel. Although width and curvature increased the size of the damage caused by an identical energy impact, the indentation growth was delayed with respect to farfield strain (stress). Because indentation growth is chiefly a local phenomenon, the delay was probably due to the variations in the damage state. The baseline specimen (flat, 83 mm in width) serves as an adequate coupon-level test even though it is conservative when compared to wider plates.

Keywords

damage tolerance sandwich structures barely visible impact damage CAI curvature scaling effects

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